My data set sometimes contains multiple observations for the same year as below.
id country ccode year region protest protestnumber duration
201990001 Canada 20 1990 North America 1 1 1
201990002 Canada 20 1990 North America 1 2 1
201990003 Canada 20 1990 North America 1 3 1
201990004 Canada 20 1990 North America 1 4 57
201990005 Canada 20 1990 North America 1 5 2
201990006 Canada 20 1990 North America 1 6 1
201991001 Canada 20 1991 North America 1 1 8
201991002 Canada 20 1991 North America 1 2 5
201992001 Canada 20 1992 North America 1 1 2
201993001 Canada 20 1993 North America 1 1 1
201993002 Canada 20 1993 North America 1 2 62
201994001 Canada 20 1994 North America 1 1 1
201994002 Canada 20 1994 North America 1 2 1
201995001 Canada 20 1995 North America 1 1 1
201995002 Canada 20 1995 North America 1 2 1
201996001 Canada 20 1996 North America 1 1 1
201997001 Canada 20 1997 North America 1 1 13
201997002 Canada 20 1997 North America 1 2 16
I need to sum up all values for the same year to one value per year. So that I receive one value per year in every column. I want to iterate this through the whole data set for all years and countries. Any help is much appreciated. Thank you!